The invention relates to presses for forming workpieces. The invention relates more particularly to a forming press useful for bending sheet metal workpieces, and suitable for use in a single-part-flow manufacturing line such as a Chaku Chaku type of manufacturing line.
Traditional batch style of manufacturing calls for large batches of workpieces to be processed at each of a plurality of work stations. At each work station, a large batch of workpieces is processed, and when all of the workpieces in the batch are completed, the batch is transported to the next work station, where a different work operation is performed on each of the workpieces in the batch, and so on, until the batch has moved through all of the work stations on the manufacturing line. Efficiency and productivity studies have shown that in some applications this batch style of manufacturing is inefficient, and that significant improvements in efficiency and productivity can be attained by instead using a single-part-flow style of manufacturing.
In the single-part-flow manufacturing line, a number of work stations are arranged in close proximity to each other so that an operator can easily access each work station with minimal walking or movement required to get from one work station to the next. For example, a number of different machines can be arranged in a U-shaped cell with the operator in the middle. One such manufacturing method is sometimes referred to as a Chaku Chaku type of process. xe2x80x9cChaku Chakuxe2x80x9d is a Japanese terms that means xe2x80x9cload load.xe2x80x9d In a Chaku Chaku line, the machines are typically designed such that the operator can load a workpiece into a machine and turn the machine on so that the machine begins its process, and the machine will automatically complete its process without further intervention of the operator. The operator picks up the completed workpiece processed by a given machine, loads a new workpiece into that machine, and starts the machine. The operator then takes the completed workpiece, loads it into the next machine in the line, picks up the previously completed workpiece from that machine, and starts the machine. The process continues down the line. Thus, a given workpiece flows from machine to machine in a very synchronized manner, and does not have to traverse a great distance during the process.
To facilitate this Chaku Chaku style of manufacturing, it should be apparent that it is desirable for a given machine in the line to be automatically operable to as great an extent as possible. It should be relatively easy for the operator to remove a completed workpiece from the machine and to load a new workpiece into the machine. The loading and removal process are performed manually by the operator in many such machines, thus requiring the operator to place his or her hands near moving parts of the machine. Thus, while accessibility to the machine by the operator is essential, safety must also be a key consideration in the design of the machine. Conventional brake presses used for bending sheet metal often require the operator to place his or her hands near the moving press tooling during press operation, thereby compromising safety.
The present invention was developed for use in a single-part-flow environment for forming metal workpieces such as sheet metal parts, and particularly for three-point bending of sheet metal blanks. The invention provides a press having features enabling a workpiece to be held and positioned properly with respect to the tooling without any assistance by the operator once the workpiece is loaded into the press, and enabling a completed workpiece to be automatically discharged from the press following the completion of a machine cycle. Preferred embodiments of the press also include safety features ensuring that the area near the moving tooling cannot be accessed by the operator during a machine cycle.
To these ends, a press in accordance with a preferred embodiment of the invention includes a press frame, a stationary press member mounted to the frame and supporting a lower forming tool, and a reciprocating press member movably supported by the frame above the stationary press member so as to be movable toward and away from the stationary press member. The reciprocating press member supports an upper forming tool positioned such that the upper and lower tools engage the workpiece therebetween and deform the workpiece when the reciprocating press member is lowered to the bottom of its stroke. The press also includes a drive system for causing the reciprocating press member to execute a stroke, and a tilting table disposed between the stationary and reciprocating press members. The tilting table has a generally planar support surface adapted to support the workpiece thereon. The tilting table is linked to the reciprocating press member such that it pivots during a stroke of the reciprocating press member, starting out in an inclined position when the reciprocating press member is at the top of its stroke, but pivoting into a horizontal position just before the reciprocating press member reaches the bottom of its stroke and the upper forming tool engages the workpiece. When the reciprocating press member returns to the top of its stroke, the tilting table is pivoted back upward such that the support surface becomes inclined and the finished workpiece is carried by gravity downward along the support surface and is automatically discharged from the press. A bin may be provided for catching the discharged workpiece. Preferably, the tilting table includes a fixture jig for positioning a workpiece on the support surface so that the workpiece is in the proper location relative to the forming tools. The fixture jig can comprise a stop member positioned on the tilting table so that gravity urges the workpiece down the inclined support surface of the tilting table and against the stop member. Advantageously, a spring device can be provided on the tilting table for urging the workpiece against the stop member of the fixture jig if gravity alone is not sufficient to ensure that the workpiece remains against the stop member until the forming tools engage the workpiece.
In accordance with a preferred embodiment of the invention, the tilting table defines an aperture therethrough over which the workpiece is positioned. The tilting table is disposed such that when it is pivoted down into the horizontal position, the tilting table surrounds the lower forming tool and the upper forming tool passes through the aperture to engage the workpiece between the forming tools. A flexible diaphragm preferably spans the aperture. The diaphragm protects the workpiece against marring or marking by the lower forming tool, and prevents the workpiece from falling through or becoming lodged in the aperture and thus facilitates the automatic discharging of the workpiece from the press.
The tilting table is linked to the reciprocating press member by a lifting linkage affixed to the reciprocating press member and extending downward therefrom. The linkage engages and lifts one end of the tilting table when the reciprocating press member moves upward toward the top of its stroke. Advantageously, the lifting linkage includes a roller at a lower end thereof, the roller engaging a lower surface of the tilting table. The tilting table preferably is arranged to pivot downward during the downward stroke of the reciprocating press member until the tilting table abuts a hard stop that stops the handler in a horizontal position. The press preferably is configured so that the tilting table reaches the horizontal position a short time before the reciprocating press member reaches the bottom of its stroke; as the reciprocating press member continues toward the bottom of its stroke, the roller of the lifting linkage disengages from the tilting table. The roller re-engages the tilting table as the reciprocating press member starts back up toward the top of its stroke and lifts the tilting table back to the inclined position for discharging the finished workpiece.
In another preferred embodiment of the invention, the press includes a safety door movable between an open position allowing operator access through the front side of the press to the lower forming tool and a closed position preventing such access. The door is closed prior to the forming tools coming together to deform a workpiece, and is opened again after the workpiece is deformed and the reciprocating press member returns to the top of its stroke. The press includes an actuator system for automatically moving the safety door to the closed position prior to the upper forming tool being lowered into engagement with the lower forming tool. The actuator system includes a fluid supply device linked to the reciprocating press member such that downward movement of the reciprocating press member forces fluid under pressure from the fluid supply device, and a fluid-powered actuator connected to the safety door and fluidly coupled to the fluid supply device such that the fluid forced from the fluid supply device activates the actuator to close the safety door. When the reciprocating press member moves back upward, the fluid supply device forces fluid into an opposite side of the actuator so that the actuator opens the safety door. The fluid supply device and actuator advantageously can comprise pneumatic cylinders coupled together in a circuit arrangement.
The invention thus provides a unique press having features providing automated workpiece positioning and discharging of finished parts so that the operator does not have to place his or her hands near the moving parts of the press during a cycle, thereby enhancing part flow and safety. Additionally, where the press includes the automatic safety door feature, safety is further enhanced. Presses made in accordance with the present invention are especially suitable for a single-part-flow or Chaku Chaku style of manufacturing line.